MULTI-STAGE ROTARY PISTON PUMP

Abstract

A multi-stage rotary piston pump comprising two shafts in a housing, which support multiple rotary pistons. Corresponding rotary pistons form a respective rotary piston pair, wherein multiple rotary piston pairs are provided which form a respective pump stage. Neighboring pump stages are each connected to one another via connection channels. The multi-stage rotary piston pump also comprises a pump inlet that is connected to the first pump stage, as well as a pump outlet that is connected to the last pump stage. The built-in volume ratio is at least 15, so that high pumping capacities of at least 1500 m.sup.3/h can be achieved.

Claims

1. A multi-stage rotary piston pump comprising two shafts arranged in a housing and supporting a plurality of rotary pistons, wherein corresponding rotary pistons make up a rotary piston pair, and a plurality of rotary piston pairs each constituting a pump stage are provided, a plurality of connection channels each connecting neighboring pump stages to each other, a pump inlet connected to the first pump stage, and a pump outlet connected to the last pump stage, wherein the built-in volume ratio is at least 15.

2. The multi-stage rotary piston pump according to claim 1, wherein the number of stages is at least three.

3. The multi-stage rotary piston pump according to claim 2, the following applies to the number of steps: n>√{square root over (VR)}−1 .

4. The multi-stage rotary piston pump according to claim 1, wherein, for avoiding an overcompression, at least one of the pump stages is connected to a relief channel where a relief valve is arranged.

5. The multi-stage rotary piston pump according to claim 1, wherein at least the second and the third pump stages are connected to a relief valve.

6. The multi-stage rotary piston pump according to claim 4, wherein the relief channels are connected to the environment and/or the pump outlet.

7. The multi-stage rotary piston pump according to claim 1, wherein the pressure difference of neighboring pump stages is smaller than 500 mbar.

8. The multi-stage rotary piston pump according to claim 1, wherein the housing comprises cooling fins on an outside and/or cooling channels arranged in housing walls.

9. The multi-stage rotary piston pump according to claim 1, wherein the connection channels are arranged in the housing.

10. The multi-stage rotary piston pump according to claim 1, wherein the pumping capacity of the overall rotary piston pump is at least 1500 m.sup.3/h.

11. The multi-stage rotary piston pump according to claim 1, wherein for a surface of a pump chamber where a rotary piston pair is arranged and which has a time-averaged pressure of more than 200 mbar, the following applies: A>400 mm.sup.2/(m.sup.3/h)*S/VR, wherein S is the highest measured pumping capacity of the pump between final pressures of 1-50 mbar, and VR is the internal volume ratio.

12. The multi-stage rotary piston pump according to claim 1, wherein during the final-pressure operation a gas temperature measured directly behind the last stage is less than 300° C.

13. The multi-stage rotary piston pump according to claim 12, wherein during the final-pressure operation a gas temperature measured directly behind the last stage is less than 250° C.

14. The multi-stage rotary piston pump according to claim 13, wherein during the final-pressure operation a gas temperature measured directly behind the last stage is less than 200° C.

15. The multi-stage rotary piston pump according to claim 10, wherein the pumping capacity of the overall rotary piston pump is at least 2500 m.sup.3/h.

16. The multi-stage rotary piston pump according to claim 9, wherein the connection channels are arranged near the cooling channels.

17. The multi-stage rotary piston pump according to claim 2, wherein the number of stages is at least five.

18. The multi-stage rotary piston pump according to claim 1, wherein the built-in volume ratio is at least 20.

19. The multi-stage rotary piston pump according to claim 1, wherein the built-in volume ratio is at least 25.

20. The multi-stage rotary piston pump according to claim 5, wherein at least the second, the third and fourth pump stages are connected to a relief valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Hereunder the disclosure will be explained in detail on the basis of a preferred embodiment with reference to the accompanying drawing in which:

[0036] FIG. 1 shows a schematic sectional view of a multi-stage rotary piston pump according to the disclosure, and

[0037] FIG. 2 shows a schematic cross-section of a rotary piston stage comprising two teeth.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0038] A multi-stage rotary piston pump according to the disclosure comprises a plurality of pump stages 12, 14, 16, 18 in a pump housing 10. Per pump stage, two rotary pistons are provided. Corresponding rotary pistons 20 configured as two-toothed rotary pistons are schematically shown in a cross-sectional view in FIG. 2. The two rotary pistons 20 rotate in opposite directions such that gas is taken in through a gas inlet 24 in a direction indicated by an arrow 22 and is discharged through an opposite outlet 26 in a direction indicated by an arrow 28.

[0039] One rotary piston each of the rotary piston pairs is arranged on a common shaft 30 (FIG. 1). Thus the multi-stage rotary piston pump comprises two shafts 30 arranged in series in FIG. 1, said shafts being supported in the housing 10. The shafts are driven by gears 32, for example. The gas to be delivered is taken in via a pump inlet 34 and discharged via a pump outlet 36. The individual stages 12, 14, 16, 18 are respectively connected to each other via connection channels 38. Each pump stage 12, 14, 16, 18 comprises an outlet 40 through which the gas to be delivered is delivered into the connection channel 38. The outlet 42 of the last pump stage 18 is connected to the pump outlet 36. In addition, the pump stages 14, 16, 18 each comprise an inlet 44 which is respectively connected to the corresponding connection channel 38. At each inlet 44 a valve 46, 48, 50, which may be a weight-loaded ball valve, for example, is provided. Via the valves, a connection between the inlets 44 and a relief channel 52 can be established. The first stage 12 can further be connected to a bypass line not shown. Such a bypass line is connected to the outlet 40 of the first stage 12 and comprises a bypass line valve. The bypass line is usually connected to the inlet 34 of the first stage. The relief channel 52 is connected to the pump outlet 36.

[0040] Preferably, the pumping capacity of the individual pump stages decreases in the direction of delivery. In particular, the pumping capacity of a succeeding pump stage amounts to half the pumping capacity of the preceding pump stage.

[0041] At the pump outlet 36 the pressure usually is approximately 1000 mbar.

[0042] The rotary piston pump can be operated in an idealized manner according to the following table when pressure losses in valves and lines are not taken into consideration.

TABLE-US-00001 P.sub.in P.sub.1 P.sub.2 P.sub.3 V.sub.1 V.sub.2 V.sub.3 1000 1000 1000 1000 0 0 0 500 1000 1000 1000 g 0 0 250 500 1000 1000 g g 0 125 250 500 1000 g g g

[0043] The table applies to a graduation ratio of 2:1 for each pump stage, i.e. the succeeding stage has half the pumping capacity of the preceding pump stage.

[0044] Here, P.sub.in is the pressure prevailing at the pump inlet 34. The pressure P.sub.1 is the pressure prevailing at the inlet of the second stage 14 , P.sub.2 is the pressure prevailing at the inlet of the third stage 16, and P.sub.3 is the pressure prevailing at the inlet of the fourth stage 18.

[0045] The stated pressures are in mbar.

[0046] The valve V.sub.1 is the valve 46, the valve V.sub.2 is the valve 48, and the valve V.sub.3 is the valve 50. “0” means that the valve is open, and “g” means that the valve is closed.

[0047] The aforementioned values stated in the table are only exemplary. It is relevant that the pressures are halved from one stage to the next one, depending on which valves are open. Thus the pressure is always halved when the corresponding valve in the stage is closed since the stage only operates when the valve is closed.